JP2006305879A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately correct a deviation not larger than one pixel in the main scanning direction of dots (for example, beam spots) each other formed by a plurality of dot forming means (for example, a plurality of light sources). <P>SOLUTION: An image forming apparatus has two light emitting parts, and forms a plurality of screen images by controlling two light emitting parts based on image data of a plurality of kinds of screen angles stored in a screen pattern storing part 25. Among a plurality of screen images formed, based on linearity of at least one screen image, relative timing of driving clocks fed to two light emitting parts is adjusted by an accuracy smaller than one pixel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method having a plurality of means for forming dots.

In recent years, various techniques for forming an image by simultaneously scanning light beams output from a plurality of light sources have been proposed as means for realizing higher speed in image forming apparatuses such as copying machines and printers. In such a multi-beam type image forming apparatus, it is impossible to obtain a good image unless the writing start positions of the respective light beams are aligned. Therefore, in Patent Document 1, an image density difference between a first pattern repeated with 1 dot or more in the main scanning direction and a second pattern repeated with 1 dot or more in the reverse main scanning direction is detected, and the image density difference is allowed. There has been proposed a technique for adjusting the light beam lighting start timing so as to obtain a predetermined value.
JP 2004-50515 A

  However, as in Patent Document 1, in the method of detecting the deviation of the beam spot in the main scanning direction using the image density difference of a plurality of patterns, detection errors often occur, and the deviation of one pixel or less is accurately detected. There was a problem that could not be done.

  An object of the present invention is to accurately correct a deviation of one pixel or less in the main scanning direction between dots (for example, beam spots) formed by a plurality of dot forming means (for example, a plurality of light sources).

  In order to solve the above problem, the invention described in claim 1 has a plurality of dot forming means for forming dots, and the relative timing of the drive clock supplied to the plurality of dot forming means is adjusted with an accuracy smaller than one pixel. Adjusting means, storage means for storing image data of a plurality of types of screen angles, and controlling the plurality of dot forming means based on the image data of the plurality of types of screen angles stored in the storage means Control means for forming a screen image and adjusting relative timing by the adjusting means based on the plurality of formed screen images.

  The invention according to claim 2 includes a plurality of dot forming means for forming dots, an adjusting means for adjusting the relative timing of the drive clock supplied to the plurality of dot forming means with an accuracy smaller than one pixel, and a predetermined The storage means for storing screen angle image data and the adjusting means are controlled to generate different relative timings, and the image of the predetermined screen angle stored in the storage means under each of these different relative timing conditions. Control means for controlling the plurality of dot forming means based on the data to form a screen image.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the control unit adjusts the relative timing by the adjusting unit based on a plurality of screen images formed under the different relative timing conditions. It is characterized by doing.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or third aspect, the control unit performs the relative processing based on linearity of at least one of the plurality of formed screen images. It is characterized by adjusting the timing.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the image forming apparatus further includes an image reading unit that reads an image, the image reading unit reads the plurality of formed screen images, and the control unit includes: The linearity of each of the plurality of read screen images is obtained.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect of the present invention, the image forming apparatus includes an operation unit that receives an operation from an operator, and the control unit receives at least one screen by an operation input from the operation unit. It is characterized by obtaining linearity of the image.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the dot forming unit includes a light source.

  The invention according to claim 8 is based on a forming step of forming a plurality of screen images by controlling a plurality of dot forming means based on image data of a plurality of types of screen angles, and the plurality of formed screen images. And adjusting the relative timing of the drive clock supplied to the plurality of dot forming means with an accuracy smaller than one pixel.

  According to a ninth aspect of the present invention, each of the generating step of generating different relative timings by controlling the relative timing of the drive clock supplied to the plurality of dot forming means with an accuracy smaller than one pixel, and each of the different relative timing conditions And forming a screen image by controlling the plurality of dot forming means based on image data of a predetermined screen angle.

  According to a tenth aspect of the present invention, in the image forming method according to the ninth aspect, the method includes an adjustment step of adjusting the relative timing based on a plurality of screen images formed under the different relative timing conditions. It is said.

  According to an eleventh aspect of the present invention, in the image forming method according to the eighth or tenth aspect, in the adjustment step, the adjustment step is based on linearity of at least one of the plurality of formed screen images. The relative timing is adjusted.

  A twelfth aspect of the present invention is the image forming method according to the eleventh aspect, further comprising a reading step of reading the plurality of formed screen images, and in the adjusting step, each of the plurality of read screen images. It is characterized in that the linearity of can be obtained.

  According to a thirteenth aspect of the present invention, in the image forming method according to the eleventh aspect, in the adjusting step, the linearity of at least one screen image is obtained by an operation input from the operation means by the operator. It is said.

  The invention described in claim 14 is the image forming method according to any one of claims 8 to 13, wherein the dot forming means includes a light source.

  According to the present invention, highly accurate calibration can be realized with a simple configuration, and image quality can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
First, the configuration in the present embodiment will be described.

  FIG. 1 shows a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 is, for example, a copying machine, a printer, or the like. The image forming apparatus 100 scans a laser beam onto the photosensitive drum 1 to form an electrostatic latent image, the photosensitive drum 1, and the photosensitive drum 1. A charging unit 2 for charging the toner, a developing unit 3 for attaching toner on the photosensitive drum 1, a transfer unit 4, a cleaner 5 for cleaning the toner remaining on the peripheral surface of the photosensitive drum 1, and a photosensitive drum. It is comprised by the static elimination part 6 which neutralizes the surface of 1. The transfer unit 4 includes a transfer electrode 4 </ b> A that charges the transfer paper P to attract and transfer a toner image, and a separation electrode 4 </ b> B that discharges the transfer paper P and separates it from the photosensitive drum 1. In this embodiment, the rotation direction of the photosensitive drum 1 is a sub-scanning direction, and the axial direction (longitudinal direction) of the photosensitive drum 1 is a main scanning direction.

  In order to form an image, first, the charging unit 2 uniformly charges the surface of the photosensitive drum 1. Then, laser light from the exposure unit 10 is emitted based on image data read from the document by a scanner or the like, and a latent image is formed on the surface of the photosensitive drum 1. The developing unit 3 reversely develops the latent image and forms a toner image on the photosensitive drum 1. Then, the transfer paper P fed from a paper storage unit (not shown) is conveyed to the transfer position.

  The transfer electrode 4A is charged by the transfer electrode 4A so as to be in pressure contact with the developing surface of the photosensitive drum 1, and the toner image on the photosensitive drum 1 is attracted to the transfer paper P and transferred. Then, the charged transfer paper P is discharged by the separation electrode 4B, and the transfer paper P is separated from the photosensitive drum 1. Thereafter, the toner image is fixed on the transfer paper P by heating and pressing by a fixing unit (not shown), and is discharged from a paper discharge roller. Then, the toner remaining on the surface of the photosensitive drum 1 is removed by the cleaner 5, and the surface of the photosensitive drum 1 is made uniform by the charge removal of the photosensitive drum 1 by the charge removing unit 6. Image formation ends.

FIG. 2 shows a schematic configuration of a laser scanning optical system constituting the exposure unit 10.
As shown in FIG. 2, the laser scanning optical system includes a laser light source 11, a collimator lens 12, a slit 13, a cylindrical lens 14, a polygon mirror 15, an fθ lens 16, a cylindrical lens 17, a mirror 18, and a horizontal synchronization sensor 19. Composed. The laser light source 11 is a semiconductor laser unit having two light emitting portions 11a and 11b, and these two light emitting portions are arranged orthogonal to the main scanning direction. The mirror 18 and the horizontal synchronization sensor 19 are provided at positions outside the image forming area of the photosensitive drum 1.

  The laser light source 11 may have a configuration in which two semiconductor laser units each having one light emitting unit are provided. In the present embodiment, of the two light emitting units 11a and 11b, the light emitting unit 11a is used as a reference LD (Laser Diode), and the timing of the drive clock is controlled for the light emitting unit 11b according to the deviation of the beam spot in the main scanning direction. LD for control to be performed.

  The two light beams emitted from each of the light emitting units 11 a and 11 b are converted into parallel light beams by the collimator lens 12, and 2 emitted from the collimator lens 12 by the slit 13 for shaping the beam spot on the photosensitive drum 1. The transmission of one luminous flux is limited. The two light beams transmitted through the slit 13 are imaged by the cylindrical lens 14 on the mirror surface of the rotating polygon mirror 15 and deflected by being reflected by the mirror surface. The reflecting mirror surface of the polygon mirror 15 can be regarded as a virtual light source. Since the distance from the virtual light source to the surface of the photosensitive drum 1 varies depending on the direction of the reflecting mirror surface, the fθ lens 16 corrects the influence of the light beam emitted from the virtual light source on the main scanning speed.

  The two light beams emitted from the fθ lens 16 are imaged on the photosensitive drum 1 by the cylindrical lens 17. The scanning lines of the two light beams imaged on the photosensitive drum 1 are as indicated by La and Lb in FIG. As shown in FIG. 2, some of the two light beams reflected from the polygon mirror 15 are reflected by the mirror 18 and enter the horizontal synchronization sensor 19. The horizontal synchronization sensor 19 receives a light beam from the light emitting unit 11a as a reference LD and generates a synchronization detection signal, and the exposure start positions of the two light beams are determined based on the synchronization detection signal. In the image forming apparatus 100 including the exposure unit 10 in FIG. 2, scanning exposure (main scanning) is performed by rotation of the polygon mirror 15, and sub scanning is performed by rotation of the photosensitive drum 1, thereby forming an image.

  FIG. 2 shows a case where a polygon mirror 15 having eight mirror surfaces is used as a scanner that scans two light beams transmitted through the slit 13 in the main scanning direction, but the number of mirror surfaces constituting the scanner is shown. Is not particularly limited.

  FIG. 3 shows a main configuration of a control circuit in the image forming apparatus 100. As shown in FIG. 3, the control circuit includes a synchronization signal / CLK generation unit 20, a delay control unit 21, image write setting units 22a and 22b, image memories 23a and 23b, a light source drive control unit 24, and a screen pattern storage unit 25. , A page memory 26, a selector 27, an operation unit 28, a scanner 29, and a delay amount detection unit 30.

  The synchronization signal / CLK generator 20 receives the synchronization detection signal generated by the horizontal synchronization sensor 19 and outputs the synchronization signal 1 and the image clock signal CLK1 synchronized with the input image clock signal CLK. The synchronization signal 1 and the image clock signal CLK1 are input to the delay control unit 21 and the image write setting unit 22a.

  As described above, the light emitting units 11a and 11b are arranged orthogonal to the main scanning direction. However, when the orthogonal mounting accuracy is not obtained, as shown in FIG. In one beam spot, a shift (Δx) of one pixel (line pitch) or less occurs in the main scanning direction.

  The delay control unit 21 receives the input synchronization signal 1 and image clock signal CLK1 based on the delay amount detected by the delay amount detection unit 30 (delay amount detected according to the shift amount Δx in the main scanning direction). Adjustment (control) is performed with an accuracy within one pixel, and the synchronization signal 2 and the image clock signal CLK2 obtained by the adjustment are output to the image write setting unit 22b.

  The image writing setting unit 22a receives the synchronization signal 1 and the image clock signal CLK1, generates the writing signal 1 indicating the image effective area in the main scanning direction, and outputs it to the image memory 23a together with the image clock signal CLK1. The output of the write signal 1 is started after the clock for a predetermined pixel has elapsed after the input of the synchronization signal 1.

  The image writing setting unit 22b receives the synchronization signal 2 and the image clock signal CLK2, generates the writing signal 2 indicating the image effective area in the main scanning direction, and outputs it to the image memory 23b together with the image clock signal CLK2. The output of the write signal 2 is started after the clock for a predetermined pixel has elapsed after the input of the synchronization signal 2.

  The image memory 23a captures and stores the odd-line image data (screen pattern image data (see FIG. 7 to be described later)) input from the selector 27. When the image data for one line is accumulated, the image data is stored. , And output to the subsequent light source drive control unit 24 in the stored order. Hereinafter, the image data output from the image memory 23a is referred to as image data 1.

  The image memory 23b captures and stores the even-line image data (screen pattern image data (see FIG. 7 described later)) input from the selector 27, and when the image data for one line is accumulated, the image data is stored. , And output to the subsequent light source drive control unit 24 in the stored order. Hereinafter, the image data output from the image memory 23b is referred to as image data 2.

  The light source drive control unit 24 controls turning on / off of the light emitting unit 11a based on the image data 1 input from the image memory 23a. Further, the light source drive control unit 24 controls turning on / off of the light emitting unit 11b based on the image data 2 input from the image memory 23b.

  FIG. 5 shows an example of a timing chart of the synchronization signal 1, the image data 1, the image data 2, and the corrected image data 2. When the shift (Δx) of one pixel or less does not occur in the main scanning direction, the delay control in the delay control unit 21 is not performed, and as shown in FIGS. 5A, 5B, and 5C, the image data 1 And the image data 2 are output at the same timing from the synchronization signal 1. When the light emitting unit 11b (control LD) shifts ahead of the light emitting unit 11a (reference LD) by the time Δt, as shown in FIG. 5D, the image data 2 is delayed by a time corresponding to Δt. By doing so, it is possible to realize image formation without deviation in the main scanning direction.

  Returning to FIG. 3, the screen pattern storage unit 25 stores a plurality of types of screen angle image data (screen pattern image data). FIG. 6 shows the relationship between the shift amount in the main scanning direction, the screen angle, and the screen patterns (A to H) classified according to the screen angle. FIG. 7 shows images of patterns A to H. As shown in FIG. 7, the screen patterns A to H correspond to a 16 × 16 image area having a basic pattern of two dots of the light emitting unit 11 a (reference LD) and the light emitting unit 11 b (control LD). The basic pattern is arranged at the screen angle. When actually forming an image, as shown in FIG. 8, a plurality of (eight types in FIG. 8) screen images are formed by forming each screen pattern in a designated image output area.

  The page memory 26 temporarily stores the image data of the screen pattern read from the screen pattern storage unit 25. The selector 27 outputs the odd line image data of the screen pattern image data read from the page memory 26 to the image memory 23a, and outputs the even line image data to the image memory 23b.

  The operation unit 28 includes various operation keys such as a copy start key and a numeric keypad, and a touch panel, and outputs an operation signal by a key input or a touch instruction to the delay amount detection unit 30.

  The scanner 29 reads the image information of the document, generates a digital image signal (image data), and outputs it to the delay amount detection unit 30.

  The delay amount detection unit 30 detects a shift amount in the main scanning direction based on an operation input by the operation unit 28 or a screen image read result by the scanner 29, detects a delay amount with respect to the synchronization signal 1 and the image clock signal CLK1, The delay amount is output to the delay control unit 21. Hereinafter, a method for detecting the amount of deviation in the main scanning direction will be described in detail.

  The amount of deviation in the main scanning direction can be detected by selecting the most linear image among a plurality of screen images formed on the transfer paper. For example, when it is determined that the pattern C in FIG. 7 has linearity by visual observation of the operator or reading by the scanner 29 among the plurality of screen images, a deviation of −1/4 pixel (the control LD becomes the reference LD). If it is determined that the pattern F is linear, it is determined that there is a deviation of +1/2 pixel (the control LD is delayed by 1/2 pixel with respect to the reference LD). The

  FIG. 9A shows an output state of the patterns G and H when a deviation of −1 pixel in the main scanning direction (the control LD is one pixel ahead of the reference LD) occurs, and FIG. The output states of the patterns G and H when a shift of +1 pixel in the main scanning direction (the control LD is delayed by one pixel with respect to the reference LD) are shown. As shown in FIG. 9A, when a shift of −1 pixel occurs, it is determined that the pattern G has linearity. When a shift of +1 pixel occurs, it is determined that the pattern H has linearity as shown in FIG.

  As described above, the linearity of the screen image is determined by visual observation by the operator or image reading by the scanner 29. When determining linearity by visual observation by an operator, a signal for designating a screen image determined to have linearity by an operation input from the operation unit 28 among a plurality of screen images formed on the transfer paper is detected as a delay amount. Input to the unit 30. The delay amount detection unit 30 detects a shift amount corresponding to the designated screen image based on the table of FIG.

  When determining the linearity of the screen image by reading an image with the scanner 29, the delay amount detection unit 30 reads a plurality of screen images read by the scanner 29, converts the frequency of each screen image, and matches the two-dimensional frequency components. To obtain a screen image having linearity and detect a shift amount corresponding to the screen image.

  As described above, according to the image forming apparatus 100 of the present embodiment, one of the plurality of screen images in the main scanning direction of the beam spot by the light emitting units 11a and 11b is based on the linearity of at least one screen image. By controlling the timing of the drive clock supplied to the light emitting units 11a and 11b so as to detect the amount of deviation below the pixel and correct the amount of deviation, high-precision calibration can be realized with a simple configuration. Quality image formation can be realized.

<Modification>
By adjusting the relative timings of the drive clocks supplied to the light emitting units 11a and 11b, different relative timings are generated with an accuracy smaller than one pixel, and a predetermined (specific) screen angle is set under each of these different relative timing conditions. A plurality of screen images can be formed from the image data, and the relative timing can be adjusted based on the plurality of screen images.

  In this case, when an image is actually formed, a plurality of screen images are formed by forming screen images formed at each relative timing in a designated image output region. FIG. 10 shows an example of output areas of a plurality of screen images formed at each relative timing. In FIG. 10, the pattern G and H image data stored in the screen pattern storage unit 25 is used as image data of a predetermined screen angle, and the delay amount corresponding to ± 1 pixel is changed by 1/6 step. Show.

  When a plurality of screen images are obtained in this way, the linearity of the screen image is determined by the operator's visual observation or the scanner 29 as in the above-described embodiment, and the light emitting units 11a and 11b are determined based on the linearity. The amount of deviation of the beam spot in the main scanning direction is detected, and the relative timing is adjusted so as to correct the amount of deviation.

  In this embodiment, the laser scanning optical system in which the light emitting units 11a and 11b are arranged orthogonal to the main scanning direction has been described. However, in order to obtain the sub scanning pitch, the light emitting units 11a and 11b are sub scanned. The present invention can be applied even if it is arranged to be inclined at a predetermined angle with respect to the direction.

  In the present embodiment, the image forming apparatus using the laser light source 11 as a means for forming dots has been described. However, an inkjet method, an optical shutter such as a liquid crystal head and a PLZT head, DMD (Digital Micromirror Device), GLV (GLV) The processing of the present embodiment can also be applied when using a dot forming means with a light control head such as a Grating Light Valve.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a schematic configuration of an exposure unit (laser scanning optical system) of the image forming apparatus in FIG. 1. FIG. 2 is a block diagram illustrating a configuration of a main part of a control circuit in the image forming apparatus of the present embodiment. It is a figure which shows the beam spot by two light emission parts, and deviation | shift amount (DELTA) x in the main scanning direction. It is a figure which shows the timing chart of a synchronizing signal and image data 1 and 2. FIG. It is a figure which shows the relationship between a screen angle and a screen pattern. It is a figure which shows screen pattern AH. It is a figure which shows an example of the output image in which each screen pattern was formed in each image area. FIG. 5A is a diagram illustrating an output state of patterns G and H when a pixel shift is −1, and FIG. 8B is a diagram illustrating an output state of patterns G and H when a pixel shift is +1. It is a figure which shows an example of the output area | region of the patterns G and H at the time of changing the delay amount equivalent to +/- 1 pixel every 1/6 step.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging part 3 Developing part 4 Transfer part 4A Transfer electrode 4B Separation electrode 5 Cleaner 6 Static elimination part 10 Exposure part (laser scanning optical system)
DESCRIPTION OF SYMBOLS 11 Laser light source 11a, 11b Light emission part 12 Collimator lens 13 Slit 14 Cylindrical lens 15 Polygon mirror 16 f (theta) lens 17 Cylindrical lens 18 Mirror 19 Horizontal synchronous sensor 20 Synchronization signal / CLK generation part 21 Delay control part 22a, 22b Image writing setting part 23a 23b Image memory 24 Light source drive control unit 25 Screen pattern storage unit 26 Page memory 27 Selector 28 Operation unit 29 Scanner 30 Delay amount detection unit 100 Image forming apparatus

Claims (14)

Having a plurality of dot forming means for forming dots,
Adjusting means for adjusting the relative timing of the drive clock supplied to the plurality of dot forming means with an accuracy smaller than one pixel;
Storage means for storing image data of a plurality of types of screen angles;
Based on the image data of a plurality of types of screen angles stored in the storage unit, the plurality of dot forming units are controlled to form a plurality of screen images, and based on the formed plurality of screen images, the adjusting unit Control means for adjusting the relative timing;
An image forming apparatus comprising: Having a plurality of dot forming means for forming dots,
Adjusting means for adjusting the relative timing of the drive clock supplied to the plurality of dot forming means with an accuracy smaller than one pixel;
Storage means for storing image data of a predetermined screen angle;
The adjustment means is controlled to generate different relative timings, and the plurality of dot forming means are controlled based on the image data of the predetermined screen angle stored in the storage means under each of these different relative timing conditions. And a control means for forming a screen image,
An image forming apparatus comprising:   The image forming apparatus according to claim 2, wherein the control unit adjusts the relative timing by the adjusting unit based on a plurality of screen images formed under the different relative timing conditions.   The image forming apparatus according to claim 1, wherein the control unit adjusts the relative timing based on linearity of at least one of the plurality of formed screen images. Comprising image reading means for reading an image;
The image reading unit reads the plurality of formed screen images,
The image forming apparatus according to claim 4, wherein the control unit obtains linearity of each of the read screen images. An operation means for receiving an operation from the operator,
The image forming apparatus according to claim 4, wherein the control unit obtains linearity of at least one screen image by an operation input from the operation unit.   The image forming apparatus according to claim 1, wherein the dot forming unit includes a light source. Forming a plurality of screen images by controlling a plurality of dot forming means based on image data of a plurality of types of screen angles; and
An adjustment step of adjusting the relative timing of the drive clock supplied to the plurality of dot forming means based on the plurality of formed screen images with an accuracy smaller than one pixel;
An image forming method comprising: A generation step of generating different relative timings by controlling the relative timing of the driving clock supplied to the plurality of dot forming means with an accuracy smaller than one pixel;
In each of the different relative timing conditions, a forming step of controlling the plurality of dot forming means based on image data of a predetermined screen angle to form a screen image;
An image forming method comprising:   The image forming method according to claim 9, further comprising an adjusting step of adjusting the relative timing based on a plurality of screen images formed under the different relative timing conditions.   11. The image forming method according to claim 8, wherein, in the adjusting step, the relative timing is adjusted based on linearity of at least one screen image among the plurality of formed screen images. . A reading step of reading the plurality of formed screen images,
12. The image forming method according to claim 11, wherein in the adjusting step, linearity of each of the read screen images is obtained.   12. The image forming method according to claim 11, wherein in the adjustment step, linearity of at least one screen image is obtained by an operation input from an operation unit by an operator.   The image forming method according to claim 8, wherein the dot forming unit includes a light source.

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